/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.io.gcp.spanner;



import com.google.cloud.spanner.DatabaseClient;

import com.google.cloud.spanner.ReadOnlyTransaction;

import com.google.cloud.spanner.ResultSet;

import com.google.cloud.spanner.Statement;

import com.bff.gaia.unified.sdk.transforms.DoFn;



/**

 * This {@link DoFn} reads Cloud Spanner 'information_schema.*' tables to build the {@link

 * SpannerSchema}.

 */

class ReadSpannerSchema extends DoFn<Void, SpannerSchema> {



  private final SpannerConfig config;



  private transient SpannerAccessor spannerAccessor;



  public ReadSpannerSchema(SpannerConfig config) {

    this.config = config;

  }



  @Setup

  public void setup() throws Exception {

    spannerAccessor = config.connectToSpanner();

  }



  @Teardown

  public void teardown() throws Exception {

    spannerAccessor.close();

  }



  @ProcessElement

  public void processElement(ProcessContext c) throws Exception {

    SpannerSchema.Builder builder = SpannerSchema.builder();

    DatabaseClient databaseClient = spannerAccessor.getDatabaseClient();

    try (ReadOnlyTransaction tx = databaseClient.readOnlyTransaction()) {

      ResultSet resultSet = readTableInfo(tx);



      while (resultSet.next()) {

        String tableName = resultSet.getString(0);

        String columnName = resultSet.getString(1);

        String type = resultSet.getString(2);

        long cellsMutated = resultSet.getLong(3);



        builder.addColumn(tableName, columnName, type, cellsMutated);

      }



      resultSet = readPrimaryKeyInfo(tx);

      while (resultSet.next()) {

        String tableName = resultSet.getString(0);

        String columnName = resultSet.getString(1);

        String ordering = resultSet.getString(2);



        builder.addKeyPart(tableName, columnName, "DESC".equalsIgnoreCase(ordering));

      }

    }

    c.output(builder.build());

  }



  private ResultSet readTableInfo(ReadOnlyTransaction tx) {

    // retrieve schema information for all tables, as well as aggregating the

    // number of indexes that cover each column. this will be used to estimate

    // the number of cells (table column plus indexes) mutated in an upsert operation

    // in order to stay below the 20k threshold

    return tx.executeQuery(

        Statement.of(

            "SELECT"

                + "    c.table_name"

                + "  , c.column_name"

                + "  , c.spanner_type"

                + "  , (1 + COALESCE(t.indices, 0)) AS cells_mutated"

                + "  FROM ("

                + "    SELECT c.table_name, c.column_name, c.spanner_type, c.ordinal_position"

                + "     FROM information_schema.columns as c"

                + "     WHERE c.table_catalog = '' AND c.table_schema = '') AS c"

                + "  LEFT OUTER JOIN ("

                + "    SELECT t.table_name, t.column_name, COUNT(*) AS indices"

                + "      FROM information_schema.index_columns AS t "

                + "      WHERE t.index_name != 'PRIMARY_KEY' AND t.table_catalog = ''"

                + "      AND t.table_schema = ''"

                + "      GROUP BY t.table_name, t.column_name) AS t"

                + "  USING (table_name, column_name)"

                + "  ORDER BY c.table_name, c.ordinal_position"));

  }



  private ResultSet readPrimaryKeyInfo(ReadOnlyTransaction tx) {

    return tx.executeQuery(

        Statement.of(

            "SELECT t.table_name, t.column_name, t.column_ordering"

                + " FROM information_schema.index_columns AS t "

                + " WHERE t.index_name = 'PRIMARY_KEY' AND t.table_catalog = ''"

                + " AND t.table_schema = ''"

                + " ORDER BY t.table_name, t.ordinal_position"));

  }

}